1. Field of the Invention
The present invention relates to a method for adjusting the reference position of a resolver that is arranged at an end of a shaft for detecting the rotation angle of a rotor.
2. Description of the Related Art
In the past, in order to adjust the reference position of a resolver with respect to a rotor, a predetermined level of current is first supplied to a three-phase motor with its two phases short-circuited with each other thereby to stop the three-phase motor at its reference position, and the rotation angle of the rotor at that time is detected by the resolver, whereby the reference position of the resolver is adjusted from the value of the rotation angle of the rotor thus detected at the only one location (see a first patent document: Japanese patent application laid-open No. 2001-128484).
In such a known resolver reference position adjustment method, the reference position of the resolver is adjusted in such a manner that an error in the rotation angle of the rotor detected by the resolver becomes zero in the reference position of the rotor, i.e., the error of the detection value of the resolver becomes zero when the rotation angle of the rotor is zero, as shown in FIG. 12.
However, though the error of the detection value detected by the resolver with respect to the rotation angle of the rotor is generally of a sinusoidal waveform, an error amplitude D1 on a positive (+) side and an error amplitude E1 on a negative (−) side are not equal to each other, as shown in FIG. 12. Accordingly, there is a problem that in case where the reference position of the resolver is adjusted according to this method, the rotation angle of the rotor has to be detected while leaving a rotation angle region (i.e., a range around D1) in which a large error will be generated when seen over the entire rotation angle region of the rotor (0 degrees to 360 degrees).